Displays of solidity

Three-dimensional moving images have long been the stuff of science fiction. In reality, the appearance of three dimensions is usually approximated by manipulating light, but such approaches have limitations such as narrow viewing angles and the need for special viewing headwear. Daniel Smalley and colleagues offer a solution in which a three-dimensional object can be represented in real space, viewed from any angle, and even coexist with—and wrap around—solid objects that occupy the same physical volume. A near-invisible light field traps and moves a small particle through a volume of space. As the particle moves, it is illuminated using red, green and blue laser light, producing an arbitrarily coloured point-source that maps out the surface of the object to be imaged. If the particle scanning is fast enough, persistence of vision, which results from the slower ‘refresh rate’ of the human eye, gives the appearance of a solid three-dimensional surface. At even faster scanning rates, the imaged object can appear to move.